Fluid operated device



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INVENTOR. Jaw .5. 2177 021.

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.J. D. SNITGEN Filed March 8, 1967 FLUID OPERATED DEVI CE \QNx Nm Nov.12, 1968 United States ABSTRACT OF THE DISCLOSURE This applicationdiscloses a fluid operated device for applying force to a workpiecethrough a force applying member that is first moved at a relativelyrapid rate of speed toward the workpiece and which it is capable ofapplying a relatively low force against the workpiece, and whichsubsequently and automatically upon encountering the workpiece moves ata substantially slower rate but applies a substantially higher force.The device is comprised of a first fluid motor having a piston that isactuated by air pressure. This piston is connected to a substantiallysmaller piston of a hydraulic pump to displace fluid from a pumpingchamber into a second fluid motor chamber for moving a piston of asecond fluid motor that is connected to the force applying member andwhich has a substantially greater area than the pump piston. A springbiased connection is provided between the pump piston and the piston ofthe second fluid motor for simultaneous movement of the piston of thefirst fluid motor, the piston of the fluid pump and the piston of thesecond fluid motor upon the initial introduction of the air pressure tothe first fluid motor. This effects the rapid movement of the forceapplying means to a first position. When this first position is reachedand the workpiece is engaged, the spring yields causing the displacementof fluid from the fluid pump to the second fluid motor to effect asubstantial force amplification.

Background of the invention This invention relates to a fluid operateddevice and more particularly to an improved fluid operated device thatis adapted to apply an intensified force against a workpiece.

In many instances a force applying element is brought into engagementwith a workpiece and subsequently exerts a force against the workpiece.For example, in a punch press the punch engages and pierces a workpiece,in a spot welding apparatus one or both of the welding electrodes engageand apply pressure against a workpiece, and so on. Other examplesinclude devices for locking, holding, clamping or pinching workpieces,jacks, or any other devices utilizing a power cylinder wherein it isdesired to apply a relatively small force when encountering a relativelysmall resistance and a considerably higher force when the resistanceincreases. With each type of apparatus, it is desirable to have theworkpiece engaging element move rapidly into its initial engagement withthe workpiece. It is, however, necessary in many instances to apply aconsiderable force against the workpiece once it is engaged. It isdiflicult to achieve these high forces as well as the rapid movementwithout extremely high power requirements or without extremelycomplicated or large machinery or without damaging the workpiece byengaging it at tOo high a speed with too high a force.

It is, therefore, a principal object of this invention to provide afully self-contained relatively compact and simple force magnifying orintensifying device.

It is another object of this invention to provide a fluid operateddevice having a force applying member that is rapidly moved intoengagement with a workpiece and which subsequently exerts a substantialforce against the atent O 3,416,689 Patented Nov. 12, 1968 workpiece. Arelated object concerns the provision of such a device also having apowered return stroke.

Summary of the invention A fluid operated device embodying thisinvention is particularly adapted to apply force to a workpiece. Thedevice includes a first fluid motor composed of first and second memberssupported for relative movement in a first direction under the influenceof a fluid force. A fluid pump composed of third and fourth memberssupported for relative movement in a first direction and adapted todisplace fluid upon this relative movement is associated with the firstfluid motor. A second fluid motor com prised of fifth and sixth memberssupported for relative movement in a first direction upon the exertionof a fluid pressure thereto is adapted to receive the fluid transferredfrom the fluid pump upon relative movement of its members in the firstdirection through fluid passage means. The second fluid motor and fluidpump are proportioned to effect substantially less relative movementbetween motor members upon the fluid transfer through the fluid passagemeans than the relative movement occurring between the pump members fora force amplification between the fluid pump and the second fluid motor.Means operatively connect the first and third members for simultaneousmovement and means operatively connect the fourth and fifth members forsimultaneous movement. Force applying means are operatively connected tothe fifth member for its movement upon movement of the fifth member toapply force against a workpiece. Coupling means operatively connect thefirst member to the fifth member for simultaneous movement of the first,third, fourth and fifth members upon the introduction of fluid to thefirst fluid motor and until the force applying means reaches a firstposition for effecting rapid movement of the force applying means tothis first position. The coupling means is effective to provide forrelative movement between the third and fourth members upon the forceapplying means reaching its first position for displacing fluid from thefluid pump to the second fluid rnotor for movement of the force applyingmeans from the first position to a second position at a substantiallylower rate and wherein the force applying means is capable oftransmitting a substantially greater force to the workpiece than theforce generated during the movement of the force applying means to thefirst position.

Brief description 0 the drawings FIGURES 1 and 2 are cross sectionalviews taken along the longitudinal axis of a fluid operated deviceembodying this invention and showing the components in two differentpositions. FIGURE 1 shows the components before a workpiece is engaged,and FIGURE 2 shows the components subsequent to the engagement with theworkpiece.

FIGURE 3 is a cross sectional view taken along the line 3-3 of FIGURE 1.

FIGURE 4 is an enlarged view of the encircled area in FIGURE 1.

In the drawings the reference numeral 11 illustrates a fluid operated,force applying device embodying this invention. The device 11 includes aforce applying member, indicated generally by the reference numeral 12,which is adapted to engage and apply a force against a workpiece (notshown). The member 12 may carry a punch, other forming tool or maycomprise a welding electrode for spot welding. Other uses for thisdevice will suggest themselves to those skilled in the art.

The force applying device 11 is comprised of a sup porting housing 13which with internal components defines a first fluid motor, indicatedgenerally by the reference numeral 14; a fluid pump, indicated generallyby the reference numeral 15; and a second fluid motor, indicatedgenerally "by the reference numeral 16. In addition, a fluid reservoir17 is provided for the pump 15 and for the second fluid motor 16 whichare hydraulically interconnected in a manner that will become moreapparent as this description proceeds.

Thesupporting housing 13 is comprised of a first tubular cylindricalmember '18 defining a cylindrical bore 19. The tubular member 18 isclosed at one end of the cylindrical bore 19 by an end closure member 21in any suitable manner. At the other end of the bore 19, the tubularmember 18 is telescoped around a reduced diameter portion 22 of agenerally cylindrical housing member 23. This end of the tubular member18 is axially aflixed to the housing member 23 by means of a pluralityof circumferentially spaced, socket headed bolts or studs 24. Afluid-tight seal is provided between the members 18 and 23 by an O-ringseal 25 that is received within a circumferential groove 26 formed inthe housing member portion 22 and which sealingly engages the bore 19.The housing member 23, end closure 21 and member 18 define a first fluidcavity 27 which forms a part of a fluid motor 14. A generally cup-shapedpiston 28 is supported within the fluid cavity 27. The piston 28 isformed with a circumferential groove in which an O-ring seal 29 ispositioned to provide a fluid-tight seal between the bore 19 and piston28 whereby the latter divides the fluid cavity 27 into two variablevolume fluid chambers thus completing the first fluid motor 14.

A tapped opening 32 is formed in the closure member 21 for receipt of afitting 33 for introduction of fluid under pressure, for examplecompressed air or hydraulic fluid under pressure, to the fluid cavity27. For purposes of this description compressed air is used. During theadvanced stroke pressurized air is introduced on one side of the piston28 by means of a fluid passage 34 formed at the terminus of the tappedopening 32, and on the retract stroke the passage 34 is vented to theatmosphere. The portion of the cavity 27 on the other side of the piston28 is vented to the atmosphere during the advance stroke or exposed to asource of fluid pressure during the retract stroke by means of anaxially extending, fluid passage 35 formed in the housing member 23. Thepassage 35 intersects a tapped opening 37 into which a fitting 38 isthreaded. A conventional four-way valve (not shown) may be used to ventand pressurize the respective cavities, as Will become more apparent asthis description proceeds.

The closure member 21 may be formed with a cylindrical extension 41 inwhich an axially extending fluid passage 42 is formed. The fluid passage42 terminates in the outer face of the extension 41 at a tapped opening43 which may be used as an alternative location for the introduction ofair in lieu of opening 32. If not used opening 43 may be closed by aplug 44.

The piston 28 is formed with a concentric cylindrical bore 46 in whichone end of an elongated piston rod 47 is .aflixed by means of a setscrew 48. The elongated piston rod 47 has a chamfered end portion 49that is received within an axially extending bore 51 formed in anextension of the force applying member 12. The piston rod end portion 49acts as a piston and coacts with the bore 51 to form the fluid pump 15.The piston rod end 49' is formed with a circumferential groove 52 (FIG-URE 4) in which a resilient O-ring 53 is received. The O-ring 53 bearsagainst a cylindrical member 54, which is preferably formed from Teflonor some other antifriction material and urges'it into engagement withbore 51 to form a fluid-tight, low friction seal. A back-up O-ring seal55 is received in a groove in the piston rod 47 at a location spacedfrom the end 49. The seal 55 engages a cylindrical bore 56 in anenlarged cylindrical portion 57 of the force applying member 12. Theseal 55 may be of 4 the same type as shown in FIGURE 4 or may be of aconventional O-ring type.

The enlarged portion 57 of the force applying member 12 acts as a pistonand is slidably received in a cylindrical bore 61 extending axiallythrough one end of the housing member 23. The piston portion 57 has acircumferential groove 62 in which an O-ring seal 63 is received. Thepiston portion 57 and bore 61 form the second fluid motor 16 and definespaced variable volume fluid cavities 64 and 65.

A cylindrical housing member 66, which also forms a portion of thehousing 13, is telescopically received upon a second cylindricalextension of the housing member 23 and is fixed thereto bycircumferentially spaced socket headed bolts or studs 67. An O-ring seal68 is received in a groove 69 of this housing extension and sealinglyengages a bore 71 defined by the housing member 66 to effect afluid-tight seal.

The outer end of the tubular housing member 66 is closed by a. closureplug 72 in which a cylindrical bore 73 is formed. The outer end of theforce applying member 12 is piloted or slidingly supported in the bore73. An O-ring seal 74 is received in a circumferential groove 75 formedin the outer end of the force applying member 12 to sealingly engage thebore 73. The closure member 72 is axially fixed to the housing member 66by circumferentially spaced studs or socket headed bolts 76.

An outer edge of the closure member 72, indicated generally by thereference numeral 77, snugly engages the adjacent portion of the forceapplying member 12 and may act as a scraper during reciprocation of theforce applying member 12 to remove any foreign matter that tends toaccumulate thereon, such as Weld splatter which will accumulate if theforce applying member functions in a welding electrode. To assist inthis cleaning action, a wiper ring 78 is received in a groove 79 formedin the closure member 72 adjacent the edge 77.

The housing members 66 and 23 and closure member 72 coact to define thefluid reservoir 17. This reservoir is annular and encircles the forceapplying member 12. This reservoir not only accommodates for changingvolumes of fluid used by the device as it is cycled, as will become moreapparent, but also serves as a source of makeup fluid to replace thatlost through normal leakage. As a consequence devices of the presenttype are fully self-contained and may be operated for long periods oftime Without ever requiring additional fluid. To prevent the entrainmentof air in the reservoir 17, a floating annular piston 81 is received ona cylindrical extension 82 of the closed member 72. The piston 81 has acylindrical bore 83 in which an O-ring seal 84 is carried to sealinglyengage the extension 82. A second O-ring seal 85 at the outer peripheryof the piston 81 sealingly engages the bore 71 thus precluding leakagefrom the reservoir 17 past the piston 81. The back side of the piston isvented to atmosphere through normal leakage.

A plurality of circumferentially spaced coil springs 86 are received inbores 87 and 88 formed in the piston 81 and' closure member 72,respectively. The springs 86 urge the piston 81 in a direction whichtends to decrease the volume of the reservoir 17. One or morecircumferentially spaced, radially extending openings 89 are formed atthe inner end of the extension 82 and pro vide a fluid connectionbetween the reservoir 17 and the fluid cavity 65.

The fluid pump 15 is maintained in fluid registry with the cavity 64 ofthe fluid motor 16 by means of a plurality of fluid passages formed atcircumferentially spaced locations in the force applying member 12(FIGURE 3). The fluid passages 95 extend from the bore 51 into thecavity 64 through the enlarged piston portion 57. The passages 95terminate adjacent a reduced diameter cylindrical portion 96 of theforce applying member 12 on the inner end of the piston portion 57. Theportion 96 is slidably received in a bore 97 formed in the housingmember 23 and is sealingly engaged by an O-ring seal 98 received in acircumferential groove 99 formed in the member 23.

A plurality of radially extending passages 101 extend through the forceapplying member 12 adjacent the outer end of the piston portion 57.Under some circumstances, as will become more apparent as thisdescription proceeds, the passages 101 are closed by the piston endportion 49 of the piston rod 47. Preferably the passages 101 have atotal flow area equal to the flow area of the passages 95.

One end of the cylindrical extension 96 of the force applying member 12is formed with an axially extending bore 102 coaxial with the piston rod47 and extending around the latter. An enlarged diameter portion 103 ofthe piston rod 47 is received in the bore 102. The outer end of theextension 96 is threaded, as at 104, to receive a cap-shaped stop member105 having a bore 106 through which one end of the piston rod 47extends. A coil spring 107 encircles the piston rod 47 and is compressedbetween its enlarged diameter portion 103 and a shoulder 108 formed atthe base of the bore 102. The spring 107 normally urges the piston rodenlarged diameter portion 103 into engagement with the stop member 105(FIGURE 1).

Operation The sequence of operation of the force applying device 11 willbe described assuming that the force applying member 12 is a weldingelectrode for a spot welding device. It is to be understood, however,that the device is capable of use in other embodiments and thatdifferent sequences of operations may be employed. When the forceapplying member 12 functions as a welding electrode, it is preferred topreclude its rotation with respect to the supporting housing assembly 13and for this purpose a pin 111 is inserted in a bore 112 formed in thehousing member 23. The pin 111 extends into an elongated keyway 113formed in the force applying member 12 to preclude rotation during itsreciprocation. The force applying member 12 may then be connected to anysuitable source of electrical current so that it may function as a spotWelding electrode.

FIGURE 1 illustrates the force applying device 11 as it appears beforethe work engaging end of the force applying member 12 is brought intoengagement with the piece to be welded. In this position, the piston 28is at the extreme right hand side of the cavity 27 and the coil spring107 has urged the force applying member 12 to its extreme right handposition wherein the cavity 64 of the second fluid motor 16 hassubstantially little or no volume. In this position, fluid from thereservoir 17 can flow through the passage 89 into the cavity 65 as aresult of the force exerted by the spring biased piston 81. Fluid willalso fill the passages 101 and the bore 51 of the fluid pump so that thebore 51 and cavity will be completely filled with fluid.

When the device 11 is to be actuated, air under pressure is admitted tothe first fluid motor 14 through the fitting 33. At the same time, thevolume of the cavity 27 on the other side of the piston 28 is exposed tothe atmosphere by means of the valve which cooperates with the fitting38. Hence, the fluid pressure applied to one side of the piston 28 willcause it to move to the left within the bore 19. The precompression onthe coil spring 107 is chosen so that the air pressure acting upon thepiston 28 will not cause the spring 107 to yield until the forceapplying member 12 engages some resistance. Hence, the force applyingmember 12 will be moved to the left simultaneous with movement of thepiston 28 during the initial stage of operation.

The piston 28, which as has been noted, is directly coupled to thepiston rod 47, will tend to cause the piston rod end 49 to move into thebore 51. However, since the force applying member 12 is also moving inthe same direction and at the same rate of speed, there will besubstantially no displacement of fluid from the fluid pump 15. Thevolume of the fluid cavity 64 is, however, increased during this initialmovement since the piston portion 57 of the force applying member 12moves with respect to the supporting housing 13. This results in adecrease in volume of the cavity 65 and an increase in volume of thecavity 64 Since the cross sectional areas of the cavities 64 and 65 arethe same and the piston portion 57 is common to these cavities, fluidwill merely flow from the cavity 65 to the cavity 64 through first theports 101, then the bore 51 and finally through the passages 95. As hasbeen noted, the ports 101 and passages havesubstantially the same crosssectional area, hence, there will be substantially no restriction toflow. This described initial phase of movement of the force applyingmember 12 is accomplished at a relatively high rate of speed since thereis substantially no force amplification during this initial movement.

When the end of the force applying member 12 contacts a workpiece, therewill be very little force amplification exerted upon the workpiece. Suchinitial force amplification will be proportional to the ratio of thearea of the piston 28 to the area of the force applying element 12 thatcontacts the workpiece. Assuming that the workpiece is supported in arelatively unyielding manner, a resistance to further movement of theforce applying element 12 is created as soon as the workpiece isengaged. This resistance to further movement eventually will overcomethe action of the coil spring 107 and the previous coupling between thepiston rod 47 and force applying member 12 efiected by the spring 107will now yield and permit relative movement between the piston rod 47and force applying member 12( FIGURE 2). During the initial relativemovement, the piston rod end 47 will move toward the ports 101 and tendto displace fiuid from the cavity defined by the bore 51. This initialdisplacement of fluid will drive fiuid through the ports 101 into thecavity 65 and into the reservoir 17 through the port 89. This will causethe piston 81 to be displaced slightly to the left against the action ofthe coil springs 86.

Continued movement of the piston rod end 49 will bring it into registrywith the ports 101 cutting off further flow of fluid to the cavity 65-and reservoir 17 from the bore 51. Member 54 prevents abrasion of O-ring53 by the ends of bores 101. As the relative movement continues, createdby the continued application of fluid pressure on the piston 28, thepiston rod end 49 will displace fluid from the fluid pump 15 into thecavity 64 of the fluid motor 16 through the passages 95. Inasmuch as theexposed area of the piston portion 57 of the force applying member 12 isgreater than the area of the piston rod end 49, there will be a fluidamplification in the fluid force exerted upon the force applying member12 by the fluid motor 16. This force amplification is achieved becauseof the noted difference in areas and results in a substantially lessermovement of the force applying member 12 than the movement of the piston28. A considerably higher force is exerted, however, upon the workpieceby the force applying member 12 during this stage of operation. As theforce applying member 12 moves relative to the housing assembly 13during this movement, the volume of the fluid chamber 65 will bedecreased. The fluid displaced from the chamber 65 cannot, however, flowinto the chamber 64 since the ports 101 have been closed by the pistonrod end 49. The fluid thus displaced from the chamber 65 is, however,transferred into the fluid reservoir 17 through the ports 89. Thisnecessitates an increase in the volume of the reservoir 17 which isaccomplished by displacement of the piston 81 against the action of thecoil springs 86.

When the desired degree of pressure is exerted upon the workpiececurrent is passed through the force applying member 12 or an electrodeaflixed thereto to effect the spot weld. After the spot weld has beeneffected, the fitting 33 is vented to the atmosphere and air underpressure is introduced to the chamber 27 on the opposite side of thepiston 28 by exposing the fitting 38 to air pressure. The piston 23 thenis forced to the right within the bore 19. This relieves the compressionupon the spring 167 and the piston rod 47 can also follow the movementof the piston 28 in this direction. This permits fluid to return to thebore 51 from the fluid cavity 64 by means of the passages 95. Hence, thepiston 28 and piston rod 47 will again move to the position shown inFIGURE 1 and the force applying element 12- will be retracted at a rapidrate. During this movement, fluid is transferred from the fluid cavity64 to the fluid cavity 65 via passages 96 and ports 101. The fluidpreviously displaced into the reservoir 17 can then return into thecavity 65 and bore 51.

The action of the spring biased piston 31 within the reservoir 17 willinsure that the pump 15 and motor 16 are maintained filled withhydraulic fluid. In addition any leakage which may occur can be taken upfrom the reservoir 17 so as to reduce the necessity for refilling.

It should be readily apparent that the disclosed device is highlyeffective in permitting rapid movement of the work engaging element 12toward the workpiece. When the workpiece is engaged, continued movementwill occur at a substantially slower rate but with a very large forceamplification. In one exemplary embodiment of the invention, the piston28 has an effective area of 2.405 square inches, the piston rod end 49has .an effective area of 0.062 square inch, and the effective area ofthe piston portion 57 of the force applying member 12 is 0.475 squareinch. The spring 197 has a preload of about 42 pounds and a force of 48pounds is required to deflect this spring to a point where ports 101 areclosed. These factors will result in the force applying member 12ultimately applying a force of about 1200 pounds to the workpiece when aline pressure of 80 p.s.i. is applied to the piston 28. Other ratios maybe obtained by merely varying the areas of one or more of the severalpistons. Generally speaking, spring 107 should be preloaded to a degreein which the force necessary to cause it to further compress is slightlygreater than the force necessary to overcome friction of the variousparts as the electrode or tool, as the case may be, is advanced towardthe workpiece. This permits the force applying member to advance all theway to the workpiece while the device is in the relatively rapid orfirst stage mode of operation, whereby upon encountering the workpiecethe device may shift to the second stage high force mode of operation.

It is to be understood that various modifications are possible in themode of operation without departing from the spirit and scope of theinvention and that various other changes and modifications will suggestthemselves to those skilled in the art. Such changes in the mode ofoperation and in the structure as may suggest themselves to thoseskilled in the art are within the scope of the invention, as defined bythe appended claims.

What is claimed is:

1. A fluid operated device for applying a force to a workpiece or thelike comprising a first fluid motor comprised of first and secondmembers supported for relative movement in a first direction under theinfluence of a fluid force exerted thereupon, afluid pump comprised ofthird and fourth members supported for relative movement in a firstdirection and adapted to displace fluid from said fluid pump uponrelative movement in their said first direction, a second fluid motorcomprised of fifth and sixth members supported for relative movement ina first direction upon the exertion of a fluid pressure thereto, fluidpassage means interconnecting said fluid pump and said second fluidmotor for fluid transfer from said fluid pump upon relative movement ofsaid third and fourth members in their said first direction to saidsecond fluid motor for effecting relative movement between said fifthand said sixth members in their said first direction, said fluid pumpand said second fluid motor being proportioned to effect substantiallyless relative movement between said fifth and said sixth members uponsaid fluid transfer through said fluid passage means than the relativemovement occuring between said third and said fourth members for a fluidforce amplification between said fluid pump and said second fluid motor,means operably connecting said first and said third members forsimultaneous movement, means operably connecting said fourth and saidfifth members for simultaneous movement, force applying meansoperatively connected to said fifth member for movement upon movement ofsaid fifth member to apply a force to a workpiece upon movement thereof,and coupling means operatively connecting said first member to saidfifth member for simultaneous movement of said first, third, fourth andfifth members upon the introduction of fluid to said first fluid motorand until said force applying means reaches a first position foreffecting rapid movement of said force applying means to said firstposition, said coupling means being effective to provide for relativemovement between said third and fourth members upon said force applyingmeans reaching said first position for displacing fluid from said fluidpump to said second fluid motor for movement of said force applyingmeans from said first position to a second position at a substantiallylower rate and wherein said force applying means is capable oftransmitting a substantially greater force to a workpiece than the forcegenerated during the movement of said force applying means to said firstposition.

2. A fluid operated device as set forth in claim 1 wherein the couplingmeans includes biasing spring means effective to transmit motion fromthe third member to the fourth member until the force applying meansencounters an object to creat suflicient force for yielding of saidspring means, the yield of said spring means providing for relativemovement between said third and fourth members.

3. A fluid operated device as set forth in claim 1 wherein the fifth andsixth members define axially spaced, variable volume fluid chambers andfurther including second fluid passage means interconnecting said fluidpump with one of said chambers, the first named fluid passage meansinterconnecting said fluid pump with the other of said chambers, andmeans for precluding flow through said second fluid passage means whensaid third and fourth members move relative to each other more than apredetermined amount.

4. A fluid operated device as set forth in claim 3 further includingfluid reservoir means in direct fluid communication with the one chamberof the second fluid motor, and means for maintaining the fluid in saidreservoir under a predetermined pressure to preclude the entrainment ofair therein and to take up any loss of fluid from said fluid pump andsaid second fluid motor.

5. A- fluid operated device as set forth in claim 4 further includingmeans for introducing air under pressure to the first fluid motor foreffecting relative movement between the first and second members, saidsecond fluid motor, said fluid pump and said reservoir being filled witha liquid.

6. A fluid operated device as set forth in claim 4 wherein the fluidoperated device includes housing means defining a first cylinder whichcomprises the second member, the first member comprising a first pistonsupported for reciprocation within said first cylinder, the third membercomprising a second piston aflixed for movement with said first piston,the fourth member comprising a second cylinder in which said secondpiston is supported for reciprocation, the fifth member comprising meansdefining a third piston integrally connected to said second cylinder,the sixth member comprising a third cylinder reciprocally supportingsaid third piston, said third cylinder being defined by said housing ata point axially spaced from said first cylinder.

7. A fluid operated device for applying force to a workpiece or the likecomprising housing means defining a first cylinder bore opening throughOne end of said housing means and means defining first and second fluidclosures at opposite ends of said first cylinder bore, a first pistonsupported for reciprocation within said first cylinder bore, means forintroducing air under pressure into said first cylinder bor on oppositesides of said first piston for reciprocating said first piston withinsaid first cylinder bore, a force applying member supported forreciprocation within said housing means and having a projecting endadapted to engage a workpiece, means defining a second cylinder bore insaid force applying member concentric with said first cylinder bore, asecond piston supported for reciprocation within said second cylinderbore, means for aflixing said second piston to said first piston forsimultaneous reciprocation of said first and second pistons, biasingmeans interposed between said second piston and said force applyingmember for establishing a yieldable driving connection between saidsecond piston and said force applying member, means in said housingmeans defining a third cylinder bore, means fixed to said force applyingmember defining a third piston supported for reciprocation within saidthird cylinder bore, the effective area of said third piston beingsubstantially greater than the effective area of said second piston,first fluid passage means extending through said force applying memberfrom said second cylinder bore to said third cylinder bore on one sideof said third piston, second fluid passage means formed in said forceapplying member and extending from said second cylinder bore to saidthird cylinder bore on the other side of said third piston, and a liquidsubstantially filling said second cylinder bore, said third cylinderbore and said first and said second fluid passage means, said biasingmeans being effective to transmit movement of said first and said secondpistons into movement of said force applying member in the samedirection and at the same speed upon the application of fluid pressureto said first piston and until the resistance to movement of said forceapplying member exceeds a predetermined value, said biasing means beingeffective to yield upon the exertion of such a predetermined resistanceto movement of said force applying member for relative movement of saidsecond piston and said force applying member for displacing a fluid fromsaid second cylinder bore into said third cylinder bore on said one sideof said third piston through said first fluid passage means, said secondpiston precluding fluid flow from said second cylinder bore to saidthird cylinder bore on said other side of said third piston through saidsecond fluid passage means upon a predetermined relative movementbetween said second piston and said force applying member for generatinga force amplification upon said force applying member by the fluiddisplaced from said second cylinder bore after said predeterminedrelative movement.

8. A fluid operated device :as set forth in claim 7 wherein the closuremeans for one end of the first cylinder bore defines the third cylinderbore and further ineluding a tubular member sealingly engaged at on endwith said closure means and extending away therefrom, means defining aclosure for the other end of said tubular member, said last namedclosure means having an inwardly extending tubular portion for pilotingsaid force applying member, said tubular extension and said tubularmember defining an annular fluid reservoir, third fluid passage meansextending through said tubular extension from said fluid reservoir tosaid third cylinder bore on the other side of the third piston, and aspring biasedannular piston received within said annular fluid reservoirfor displacing fluid from said reservoir to said third cylinder borethrough said third fluid passage means.

9. A fluid operated device :as set forth in claim 7 wherein the forceapplying member has a cylindrical portion extending into the firstcylinder bore through the closure means at one end thereof, the secondpiston having a portion extending through said cylindrical portion, saidcylindrical portion of said force applying member defining an annularcavity around said second piston and in which an enlarged portion ofsaid second piston is positioned, said biasing means comprising coilspring means positioned within said annular cavity and reacting againstsaid enlarged portion of said second piston at one of its ends andagainst said force applying member at its other end.

10. A fluid operated device as set forth in claim 9 wherein the closuremeans for one end of the first cylinder bore defines the third cylinderbore and further including a tubular member sealingly engaged at one endwith said closure means and extending away therefrom, means defining aclosure for the other end of said tubular member, said last namedclosure means having an inwardly extending tubular portion for pilotingsaid force applying member, said tubular extension and said tubularmember defining an annular fluid reservoir, third fluid passage meansextending through said tubular extension from said fluid reservoir tosaid third cylinder bore on the other side of the third piston, and aspring biased annular piston received within said annular fluidreservoir for displacing fluid .from said reservoir to said thirdcylinder bore through said third fluid passage means.

References Cited UNITED STATES PATENTS 3,266,415 8/1966 Palmer -52 XR3,276,206 10/1966 Calkins 60545 EDGAR W. GEOGH'EGAN, Primary Examiner.

